The present invention relates to an implantable pump, and more particularly to a fluid chamber structure in such a pump.
Efforts to produce heart-replacement and heart-assist devices have produced a variety of pump types and designs. One of these types is a deformable sac pump which operates by recurrent compression, or squeezing, of a deformable fluid chamber sac. A pump of this type typically consists of a disc-shaped deformable sac partially encased in a rigid housing, and an attached actuator used to compress the sac from opposite movable sides. The pump may be actuated pneumatically, by expanding and contracting fluids, by an electrical-actuated solenoid mechanism, by magnetic coupling to a driving magnet, or by other suitable driving mechanisms. The power source for the actuator is preferably external.
In any type of blood pump, the device must be constructed in size, shape and design to be readily implanted in a body cavity and to be comfortable over extended periods. The construction in the device must allow for efficient connections between the pump the vascular system near the heart. The pump must be highly reliable for long periods of continuous use. Specifically, the actuator mechanism in the pump must be efficient, long-lasting, and relatively smooth working. The chambered part of the pump--which in the case of a deformable-sac pump, includes the deformable sac itself--must be constructed to operate over long periods of continuous use with minimum stress-related fatigue and creasing. The sac design and operating characteristics must minimize thrombus formation in the fluid-containing portions of the pump. Additionally, the sac itself should be easy and relatively inexpensive to manufacture and incorporate into a rigid housing portion of the pump.
U.S. Pat. No. 4,167,046 discloses a deformable sac blood pump which solves or minimizes a number of problems associated with previously developed deformable sac blood pumps. The pump of that invention is composed of a disc-like deformable sac having an annular side wall and a pair of opposed circular walls which are adapted to be recurrently and sychronously moved toward one another, through the action of a pair of opposed pusher plates to produce pumping action. Inlet and outlet conduits in the sac are arranged to direct inlet and outlet flow substantially tangentially with respect to the annulus formed by the inner surface of the sac's annular side wall. The inlet and outlet conduits are disposed on either side of the pump region occupied by the pump actuator, producing a space-conserving arrangement of pump components. The sac itself is formed as a unitary seamless article from flexible resiliant material, providing a smooth interior sac surface which acts to prevent thrombus formation in the pump.
An object of the present invention is to provide in a deformable sac blood pump, a chamber structure which incorporates many of the advantageous features known in the prior art, including those of the pump described in the above-discussed patent, and which provides a number of unique and hitherto unknown features which enhance pump reliability and operational characteristics.
A more specific object of the invention is to provide in such a structure a deformable sac having flexing zones which are circumferentially uniform, preferably being entirely defined by machined elements.
A related object of the invention is to provide such a structure in which flexing of the sac during pump operation occurs primarily by a smooth rolling action in the flexing portions of the sac.
Yet another object of the invention is to provide such structure in which creasing and stress-related fatigue in the deformable sac are minimized.
Another object of the invention is to provide such structure designed to produce, during pumping operation a circular flow action which substantially reduces the degree of thrombus formation on inner sac surfaces.
It is still another object of the invention to provide such a chamber structure having a reduced thickness.
The novel chamber structure of the invention comprises, broadly, a deformable sac having an annular side wall which is held in a rigid condition, and a movable wall joined to the side wall through an outwardly convex flexible wall portion. A pusher plate acting against the movable wall has an initial deflection position at which the flexible wall portion takes the form of a circumferentially uniform, outwardly convex roll having a bulged cross sectional curvature. The roll maintains its circumferential uniformity and bulge-like character as the pusher plate is moved toward inwardly displaced positions to expel fluid from the sac.
In a preferred embodiment of the invention, the annular side wall is held in a rigid condition by attachment to curved inner wall portions of a rigid housing ring. The sac includes a pair of opposed, substantially parallel circular movable walls disposed on opposite sides of the housing ring, each wall being joined to the side wall by an outwardly convex flexible wall portion. A pair of pusher plates acting against associated circular walls are coordinately movable from such initial deflection positions to inwardly moved positions under the control of an actuator in the pump.
These and other objects and features of the present invention will become more fully apparent when the following detailed description of the invention is read in conjunction with the accompanying drawings.